Reducing Understeer In A Track Car

[No Crust Racing]

Hi guys, I've noticed that after a number of hot laps the car will want to understeer at Winton, most notably through the left handed sweeper and coming out of the cleavage up the back. I realise some of this will be due to overheating the tyres, and I'm playing with pressures at present but I'm also interested to know what else I can do to increase outright front grip, not just increase the time before the tyres start to go off and get greasy.

Car is as follows.

S13, CA18DET, mild mods for around 165rwkw, mild weight reduction, rear interior removed air con and stereo fully removed, battery in the boot passenger side.

- Car has BC BR Coilovers (8kg front 6kg rear).

- Damper is currently set on 4 clicks from softest of 32 settings up front but I'm playing with this as the harder I go damper, the less roll I have but the faster tyres go off, lowering the hot pressure seems to negate this though. I wold not say the car rolls excessively as is evidenced by tyre wear (see below). Rear damper is softer for max power down, also has C-West wing (rear grip is no issue what so ever).

- Tyres are Federal 595 RS-R 235/45/17 (8" front, 9" rear rims). Last tested at 36psi hot front and rear. Ran a PB by 3 tenths compared to old RE55s so grip is reasonable from these.

- Car has approx -2.2-2.3 camber up front, -1 at rear.

- 0 toe up front, few mm total toe in at the rear (somewhat due to an ever so slighty bent toe arm which are getting replaced).

- 5-6 deg castor front.

- Basic strut brace up front, none in the rear

- Standard sway bars (suspect replacing this could help but as the spring rates are already quite high for an S13 it may not be required)

- S15 power steering rack and super pro bushes, good condition tie rods etc

- From an aero point of view, I have a standard CA front bar with some venting cut into both sides for oil cooler and CAI, the lower edge does taper back towards the car on an angle so a small amount of lift could be generated there possibly.

I suspect I need to focus more on mechanical grip rather than aero as the car is only entering the left handed sweeper at about 130km/h.

I realise going back to R-Comps will help to some degree but at this point that is not an option as the RS-Rs are cheap, have decent grip and, are only 2 track days old.

What can I do suspension wise to improve front end grip? Initial turn in is good, it's mid corner and exiting when I'm trying to get on the gas as early as possible that I start to see understeer. I'm interested in tuning the current setup or replacing stock parts, not replacing already upgraded parts.

Is it worth me knocking up front splitter and undertray for the front of the car? Do I need more camber perhaps? Tyre wear looks good and it is not feathering the outside edges that I can see.

Hopefully that's enough info. if you need to know anything else let me know.

Cheers

[blind_elk]

Understeer is basically a lack of grip at the front, or, conversely TOO MUCH grip at the rear.

Standard sway bars (suspect replacing this could help but as the spring rates are already quite high for an S13 it may not be required)

You shouldn't use springs / shocks to control body roll - that's what sway bars are for. So, use a slightly stiffer REAR bar.

Take a bit of camber from the REAR - drop to maybe -0.5 deg neg.

Maybe soften off the front springs a bit.

[boostn0199]

I would put some toe out in the front start with 1 or 2 mm.

[GTSBoy]

Absolutely add some rear bar and/or lighten the front bar. In fact, take the front bar off the car (or just disconnect it and tie it up out of the way) and go for a drive - see if you surprise yourself about how big a change to bar stiffness you need to make before you notice it. It will probably be far too big a change and oversteer a lot, but you'll get the idea pretty quickly.

[Risking]

Why would you take camber out of the rear if it's understeering on a heated tire??

Spring rates are too high for an S13 on a R or RS comp tire.

A firm chassis is forced to use it's tire for lateral grip instead of it's own compliance.

The other major thing wrong with the setup you've explained which wasn't mentioned above is the lack of any toe on the front.

Toe the front out .8-1.0mm static. Typically on a Nissan with good bushings you will end up with 1.2-1.5mm out dynamic and .5-.6mm out under brakes.

Toe out will increase the initial turn in and make the direction change very precise. It will also help the chassis take a set on the spring and shock mid corner as the inner tire creates a sharper turn radius for the rear to pivot around. It does work the tire a little harder so you may want to increase front camber .5 and the rear use 1mm neg.

I'd bet with tire pressures those basic changes to allignement it will be 10 times better

[Dan_J]

I would put some toe out in the front start with 1 or 2 mm.

toe out? wouldn't this create under steer.....

[No Crust Racing]

So the consensus appears to be along the lines of this.

Adjust for some toe out up front, up to around 1mm (each side or total static?)

Replace the factory sway bars so I'm not relying on the spring rates/damper settings to control body roll

I can't easily change spring rates so they will have to stay, this is just budget club sport after all.

I think I'm at the max of the front camber, I may be able to get it up to around -2.5 but I don't think going heaps more camber is the answer as my corner speeds aren't "that" high and if the car isn't leaning over enough I'll be chewing out inside edges.

If I recall correctly, I think R32 GTS-T or GT-R factory front sway bars fit S13's and are a nice upgrade.

I also need to get some toe arms to correct the toe in at rear, as I understand it it should be 0 or at the most 1mm total static toe in for stability, at present it's a bit more than that due to aforementioned toe arm damage.

Thoughts?

[The Bogan]

http://www.trackpedi...wiki/Understeer

Some reading and stuff

[No Crust Racing]

Will have to read over lunch, bit long to read on the clock.

Something I had stupidly overlooked though is perhaps my entry speed is too high for the car setup, but that's why I want to adjust the setup so I can take the corner faster. This will be especially important when I upgrade my turbo for more killer wasps.

[No Crust Racing]

It does work the tire a little harder so you may want to increase front camber .5 and the rear use 1mm neg.

I'd bet with tire pressures those basic changes to allignement it will be 10 times better

Just on that, you mean rear toe 1mm total static?

[Risking]

I always refer to totals and static.

[No Crust Racing]

What are your thoughts on running more front camber and replacing the stock front sway bar?

[MrStabby]

What are your thoughts on running more front camber and replacing the stock front sway bar?

Getting just a stiffer front sway bar will promote more understeer, because it will work the front tyres harder when they're already past their limit. You need to make the rear tyres resist more of the cornering force with a stiffer rear bar. Sways bars are often the best bang for your buck suspension mod, so IMO you should get adjustables for both front and rear, and play with the balance. If you're really tight, just get the rear bar.

I got the whitelines for my GTR, the front is on full soft and the rear full hard, to get as much understeer out as possible. This compliments the attessa tweaker which pushes more power to the front (so more tendency for understeer).

[bubba]

Stiffer front swaybar will induce more understeer, as mentioned above you probably want to go stiffer on the rear.

On the topic of swaybars, you will find the 32GTSt (RWD platform) has a bigger front than rear whereas the 32GTR (AWD) will have a bigger rear than front.

[GTSBoy]

A related anecdote - My R32 came with front and rear bars that I never paid any attention to, thinking that they were standard. They may in fact have been standard - I haven't checked to see what the standard front bar size is. But I get ahead of myself. The whole time I have had my car (many years) I've been sufferring from enough understeer to be annoying, and have fiddled around the edges with changing stuff to try to dial it out. It turned in well, but loved a mid corner understeer. Recently I bit the bullet and bought the 24mm adjustable Whiteline bar for the rear. Suspected that it might be too big, but was willing to try it. Got the original bar off and it was tiny - like 14mm or something. That's the standard auto rear bar. Car used to be auto. Put the 24mm bar in, and it was like night and day. The understeer was gone. And it didn't become a tail happy monster either. Put the verniers on the front bar and it's like 22mm. It's no wonder the car liked to understeer. And it's no wonder that it took the 24mm bar without upsetting things. Tyre life has improved quite a lot too. No front end scrubbing and no provoked power oversteer to try to counter it when having fun = nicer treatment of tyres.

[Duncan]

put good, new semi slicks on it then report back.

[Tangles]

keep playing with the tyre pressure some more.

probably want the fronts a little lower if it seems to be understeering.

drop front damper (suspension) to lowest point and work up a click at a time from there